In critically important mechanical devices, such as life support systems in aircraft or medical equipment, continuous operation may be provided by redundant systems. For example, two electric motors may be coupled mechanically or controlled simultaneously to perform a function, such that each motor and its related drive circuitry are capable of individually performing the function if the other motor or drive circuitry fails.
Simple mechanical coupling of dual motors with gears for example usually includes a clutch that isolates a failed motor system from an operating motor system. To do otherwise would impose a drag or load on the operating motor, thereby reducing efficiency and available torque. When permanent magnet electric motors are used in such drive systems, the rotor of the failed system rotating in the stator can still act as an electric generator inducing current in the motor windings as a result of the rotating magnetic field (i.e.: electromagnetic drag).
However, the inclusion of any mechanical, magnetic or hydraulic clutch introduces system reliability concerns, mechanical complexity, weight, increased bulk, maintenance and increased costs. Particularly where high speed electric motors are used in aircraft applications, the relative increase in weight and complexity due to inclusion of a clutch system may be prohibitive.
It is an object of the present invention to provide improved means for isolating a failed electric machine, motor/generator, drive circuit or failed phase in a multiphase motor/generator in a mechanically coupled system.
Further objects of the invention will be apparent from the disclosure, drawings and description of the invention below.